Method of producing image display device and resin dispenser

ABSTRACT

Method of producing an image display device in which an image display member and light-transmitting cover member having principal surface portion and circumferential edge portion on which a light-shielding layer is formed with a step portion formed between the principal surface portion and the circumferential edge portion are laminated through light-transmitting resin layer formed from a liquid optical resin composition so a light-shielding layer formed surface of the light-transmitting cover member is arranged to face the image display member, when a resin dispenser is moved from one end of the light-shielding layer formed surface of the light-transmitting cover member toward the other end applying the liquid optical resin composition to the light-shielding layer formed surface of the light-transmitting cover member, the application amount of optical resin composition is changed on the principal surface portion of the light-shielding layer formed surface of the light-transmitting cover member and on the light-shielding layer.

This application is a Divisional Application of U.S. patent applicationSer. No. 15/493,940, filed on Apr. 21, 2017, which in turn is aDivisional Application of U.S. patent application Ser. No. 14/443,515,filed on May 18, 2015 (now U.S. Pat. No. 9,651,807 issued May 16, 2017),which in turn is a National Phase Application of PCT/JP2013/083564,filed on Dec. 16, 2013, and claims priority to Japanese Application No.2012-273945, filed on Dec. 14, 2012. The entire disclosure of each ofthe prior applications is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a method of producing an image displaydevice by bonding and laminating an image display member such as aliquid crystal display panel to a light-transmitting cover member suchas a transparent protective sheet disposed on the front side of theimage display member through a light-transmitting cured resin layer.

BACKGROUND ART

An image display device such as a liquid crystal display panel used foran information terminal such as a smartphone is produced by: placing aphotocurable resin composition between an image display member such as aliquid crystal display panel or an organic EL panel and alight-transmitting cover member; and then irradiating the compositionwith ultraviolet rays to cure the composition to thereby form alight-transmitting cured resin layer, whereby the image display memberand the light-transmitting cover member are bonded and laminated to eachother (Patent Literature 1).

Specifically, as shown in FIG. 14(A), a light-transmitting cover member20 is first prepared, and a liquid photocurable resin composition 21 isapplied to a surface 20 a of the light-transmitting cover member 20 thatis to face an image display device.

Next, as shown in FIG. 14(B), the photocurable resin composition 21applied to the surface 20 a of the light-transmitting cover member 20 isirradiated with ultraviolet rays to pre-cure the resin composition tothereby form a pre-cured resin layer 21′ (FIG. 14(C)). The pre-curing isperformed in order to render the liquid photocurable resin composition21 less flowable so that the resin composition is prevented from runningdown when the cover member is turned upside down as shown in FIG. 14(C)to thereby improve handleability.

Next, as shown in FIG. 14(D), the light-transmitting cover member 20 islaminated to an image display member 23 with the pre-cured resin layer21′ facing the image display member 23.

Next, as shown in FIG. 14(E), the pre-cured resin layer 21′ held betweenthe image display member 23 and the light-transmitting cover member 20is irradiated with ultraviolet rays to post-cure the pre-cured resinlayer 21′. An image display device 25 including the image display member23 and the light-transmitting cover member 20 that are connected throughthe light-transmitting cured resin layer 22 is thereby obtained (FIG.14(F)).

CITATION LIST Patent Literature

Patent Literature 1: WO2010/027041

SUMMARY OF INVENTION Technical Problem

When the photocurable resin composition 21 is applied to thelight-transmitting cover member 20, the photocurable resin composition21 applied must evenly cover over the entire surface 20 a of thelight-transmitting cover member 20. This is because, when thephotocurable resin composition 21 is not evenly applied, air bubbles arecaught when the light-transmitting cover member 20 is later laminated tothe image display member 23, and image distortion occurs after thelamination.

Generally, a light-shielding layer 24 is disposed on a circumferentialedge portion of the surface 20 a on the image display side of thelight-transmitting cover member 20, in order to improve the brightnessand contrast of a displayed image. Therefore, the light-transmittingcover member 20 has a step portion 26 formed between the circumferentialedge portion and principal surface portion of the surface 20 a by thelight-shielding layer 24.

Therefore, when the photocurable resin composition 21 is applied to thesurface 20 a of the light-transmitting cover member 20, protrusions 27 aand 27 b are formed on edges of the light-transmitting cover member 20and circumferential edges of the step portion 26 as shown in FIG. 15, sothat the photocurable resin composition 21 cannot be applied evenly.This is due to the light-shielding layer 24, and protrusions are formedeven when the photocurable resin composition 21 is applied to athickness larger than the height of the step portion 26.

The protrusions 27 a formed on the edges of the light-transmitting covermember 20 have no small influence on image distortion, and theprotrusions 27 b formed near the step portion 26 may cause imagedistortion because the protrusions 27 b are reflected in an image regionafter the light-transmitting cover member 20 is laminated to the imagedisplay member. When the width of the light-shielding layer 24 is small,the protrusions 27 a formed on the edges of the light-transmitting covermember 20 also influence image distortion.

Accordingly, it is an object of the present invention to provide animage display device production method in which, even when a resincomposition is applied to the surface of a light-transmitting covermember having a step portion formed thereon, the resin composition canbe applied evenly without protruding from the principal surface portionat the circumferential edges of the step portion. It is another objectto provide a resin dispenser suitable for the image display deviceproduction method.

Solution to Problem

To solve the above problems, a method of producing an image displaydevice according to the present invention is a method of producing animage display device in which an image display member and alight-transmitting cover member having a principal surface portion and acircumferential edge portion on which a light-shielding layer is formedwith a step portion formed between the principal surface portion and thecircumferential edge portion are laminated through a light-transmittingresin layer formed from a liquid optical resin composition so that alight-shielding layer-formed surface of the light-transmitting covermember is arranged to face the image display member. The method ofproducing the image display device includes: moving a resin dispenserfrom one end of the light-shielding layer-formed surface of thelight-transmitting cover member toward the other end thereof to applythe liquid optical resin composition to the light-shielding layer-formedsurface of the light-transmitting cover member; laminating thelight-shielding layer-formed surface of the light-transmitting covermember to the image display member; and curing the optical resincomposition held between the image display member and thelight-transmitting cover member, wherein the resin dispenser changes theamount of the optical resin composition applied on the light-shieldinglayer and on the principal surface portion of the light-shieldinglayer-formed surface of the light-transmitting cover member.

Furthermore, a resin dispenser according to the present invention is aresin dispenser for applying an optical resin composition to alight-shielding layer-formed surface of a light-transmitting covermember having a principal surface portion and a circumferential edgeportion on which a light-shielding layer is formed with a step portionformed between the principal surface portion and the circumferentialedge portion (the optical resin composition being held between thelight-transmitting cover member and an image display member). The resindispenser includes: a discharge port having a width larger than thewidth of the principal surface portion of the light-transmitting covermember, for discharging the optical resin composition across both thelight-shielding layer and the principal surface portion, the widthbetween opposite end portions of the discharge port that face thelight-shielding layer of the light-transmitting cover member being madelarger than the width of a central portion of the discharge port thatfaces the principal surface portion, wherein the resin dispenserdischarges the optical resin composition from the discharge port whilemoving over the light-shielding layer-formed surface of thelight-transmitting cover member in a lengthwise direction thereof.

Still further, a method of producing an image display device accordingto the present invention is a method of producing an image displaydevice in which an image display member and a light-transmitting covermember having a principal surface portion and a circumferential edgeportion on which a light-shielding layer is formed with a step portionformed between the principal surface portion and the circumferentialedge portion are laminated through a light-transmitting resin layerformed from a liquid optical resin composition so that a light-shieldinglayer-formed surface of the light-transmitting cover member is arrangedto face the image display member. The method of producing the imagedisplay device includes the steps of: moving a resin dispenser from oneend of the light-shielding layer-formed surface of thelight-transmitting cover member toward the other end thereof to applythe liquid optical resin composition to the light-shielding layer-formedsurface of the light-transmitting cover member; laminating thelight-shielding layer-formed surface of the light-transmitting covermember to the image display member; and curing the optical resincomposition held between the image display member and thelight-transmitting cover member, wherein the resin dispenser has adischarge port having a width larger than the width of the principalsurface portion of the light-transmitting cover member, for dischargingthe optical resin composition across both the light-shielding layer andthe principal surface portion, the width between opposite end portionsof the discharge port that face the light-shielding layer of thelight-transmitting cover member being made larger than the width of acentral portion of the discharge port that faces the principal surfaceportion, and wherein the resin dispenser discharges the optical resincomposition from the discharge port while moving over thelight-shielding layer-formed surface of the light-transmitting covermember in a lengthwise direction thereof.

Advantageous Effects of Invention

According to the present invention, the resin dispenser changes theamount of the optical resin composition applied on the light-shieldinglayer and on the principal surface portion of the light-shieldinglayer-formed surface of the light-transmitting cover member. In thismanner, the resin dispenser 10 can apply the optical resin compositionto the same height on the light-shielding layer 3 and on the principalsurface portion 4, so that an even coated surface can be formed over thelight-transmitting cover member 6 in its lengthwise direction. Forexample, when high protrusions are formed, the speed of moving on thelight-shielding layer is set to be higher than that on the principalsurface portion. The amount of the optical resin composition applied tothe light-shielding layer thereby becomes smaller than that to theprincipal surface portion, so that the optical resin composition can beapplied evenly.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating an image display device towhich the present invention is applied.

FIG. 2 is a perspective view illustrating the step of applying aphotocurable resin composition to the surface of a light-transmittingcover member using a resin dispenser.

FIG. 3 is a cross-sectional view of the resin dispenser.

FIG. 4 is a cross-sectional view illustrating a circumferential edgeportion of the light-transmitting cover member coated with thephotocurable resin composition.

FIG. 5 is a cross-sectional view illustrating the step of applying thephotocurable resin composition to the surface of the light-transmittingcover member using the resin dispenser.

FIG. 6 is a graph showing irregularities on the surface coated with thephotocurable resin composition in each of an Example and a ConventionalExample.

FIG. 7 is a cross-sectional view illustrating the step of irradiatingthe photocurable resin composition applied to the surface of thelight-transmitting cover member with ultraviolet rays.

FIG. 8 is a cross-sectional view illustrating the light-transmittingcover member with a pre-cured resin layer formed on the surface thereof.

FIG. 9 is a cross-sectional view illustrating the light-transmittingcover member and an image display member that are laminated through thepre-cured resin layer.

FIG. 10 is a cross-sectional view illustrating the step of furtherirradiating the pre-cured resin layer with ultraviolet rays to post-curethe pre-cured resin layer.

FIG. 11 is a cross-sectional view illustrating a resin dispenser towhich the present invention is applied.

FIG. 12 is a cross-sectional view illustrating the resin dispenser towhich the present invention is applied, when the height of a dischargeport from the surface of the light-transmitting cover member is toolarge.

FIG. 13 is a graph showing irregularities on surfaces coated with thephotocurable resin composition using the resin dispenser at differentheights.

FIG. 14 is a series of cross-sectional views illustrating a conventionalprocess for producing an image display device.

FIG. 15 is a cross-sectional view illustrating a coated surface preparedby applying a photocurable resin composition to the surface of aconventional light-transmitting cover member.

DESCRIPTION OF EMBODIMENTS

An image display device production method to which the present inventionis applied will next be described in detail with reference to thedrawings. However, the present invention is not limited only toembodiments described below. It will be appreciated that variousmodifications can be made without departing from the gist of the presentinvention. The drawings are merely schematic representations and may notreflect actual dimensional proportions etc. The specific dimensions etc.should be determined in consideration of the following description. Itwill be appreciated that dimensional relations and proportions may bepartially different among the drawings.

An image display device 1 produced by applying the present inventionincludes an image display member 2 and a light-transmitting cover member6 that are laminated through a light-transmitting resin layer 8 formedfrom a liquid optical resin composition 7, as shown in FIG. 1. In thelight-transmitting cover member 6, a light-shielding layer 3 is formedon a circumferential edge portion, and a step portion 5 is therebyformed between the light-shielding layer 3 and a principal surfaceportion 4.

Examples of the image display member 2 may include liquid crystaldisplay panels, organic EL display panels, plasma display panels, andtouch panels. The touch panel means an image display-input panelproduced by combining a display device such as a liquid crystal displaypanel and a position input device such as a touchpad.

The light-transmitting cover member 6 need only have light-transmittingproperties that allow an image formed on the image display member to bevisible, and examples thereof may include plate-shaped materials andsheet-shaped materials such as glass, acrylic resins, polyethyleneterephthalate, polyethylene naphthalate, and polycarbonate. Thesematerials may be subjected to hard coating treatment, antireflectiontreatment, etc. on one side or both sides. The thickness and physicalproperties, such as elasticity, of the light-transmitting cover member 6may be appropriately determined according to its intended purpose.

In the light-transmitting cover member 6, the light-shielding layer 3 isformed along the circumferential edge portion of a surface 6 a to belaminated to the image display member 2, and the surface 6 a includesthe principal surface portion 4 surrounded by the light-shielding layer3. The light-shielding layer 3 is provided in order to, for example,increase the contrast of an image and formed by applying a coloredcoating such as a black coating using, for example, a screen printingmethod and then drying and curing the coating. The thickness of thelight-shielding layer 3 is generally 5 to 100 μm, and this thicknesscorresponds to the step portion 5 between the light-shielding layer 3and the principal surface portion 4.

Preferably, a liquid photocurable resin composition is used for theoptical resin composition 7 applied to the surface 6 a of thelight-transmitting cover member 6 because the resin composition ispre-cured and then post-cured by irradiation with ultraviolet rays, asdescribed later. In the following description, a photocurable resincomposition 7 is used as an example of the optical resin composition. Inthe image display device 1, the photocurable resin composition 7 inliquid form is used, and the photocurable resin composition 7 is appliedto a thickness larger than the thickness of the light-shielding layer 3.This can cancel the step portion 5 formed between the light-shieldinglayer 3 and the surface 6 a of the light-transmitting cover member 6 onwhich the light-shielding layer is formed. The term “liquid (form)”means a substance that shows the viscosity measured by a cone-plateviscometer of 0.01 to 100 Pa·s (25° C.)

Preferred examples of the above photocurable resin composition 7 mayinclude a photocurable resin composition containing, as main components,an acrylate-based oligomer component (component (A)), an acrylate-basedmonomer component (component (B)), and a photopolymerization initiator(component (C)). The final curing shrinkage ratio of the photocurableresin composition 7 is 3% or higher.

The “final curing shrinkage ratio” means a curing shrinkage ratiogenerated between the photocurable resin composition 7 in an uncuredstate and the composition 7 in a completely cured state. The term“completely cured” means that the curing rate of the cured resincomposition is at least 90%, as described later. Hereinafter, the finalcuring shrinkage ratio is referred to as a total curing shrinkage ratio.The curing shrinkage ratio generated between the photocurable resincomposition 7 in an uncured state and the composition 7 in a pre-curedstate is referred to as a pre-curing shrinkage ratio. The curingshrinkage ratio generated between the photocurable resin composition ina pre-cured state and the composition in a completely cured state in apost-curing step is referred to as a post-curing shrinkage ratio.

The total curing shrinkage ratio of the photocurable resin composition 7can be computed as follows. The specific gravity of the uncuredcomposition (i.e., the composition before curing) and the specificgravity of the completely cured solid product after complete curing aremeasured using an electronic densimeter (SD-120L, manufactured by AlfaMirage Co., Ltd.), and the total curing shrinkage ratio can be computedfrom the difference in the specific gravity using the following formula.The pre-curing shrinkage ratio of the pre-cured resin product of thephotocurable resin composition 7 can be computed as follows. Thespecific gravity of the uncured composition (i.e., the compositionbefore curing) and the specific gravity of the pre-cured solid productafter pre-curing are measured using the electronic densimeter (SD-120L,manufactured by Alfa Mirage Co., Ltd.), and the pre-curing shrinkageratio is computed from the difference in the specific gravity using aformula below. The post-curing shrinkage ratio can be computed bysubtracting the pre-curing shrinkage ratio from the total curingshrinkage ratio.

Total curing shrinkage ratio (%)=[(specific gravity of completely curedproduct−specific gravity of uncured composition)/specific gravity ofcompletely cured product]×100

Pre-curing shrinkage ratio (%)=[(specific gravity of pre-curedproduct−specific gravity of uncured composition)/specific gravity ofpre-cured product]×100

Post-curing shrinkage ratio (%)=total curing shrinkage ratio−pre-curingshrinkage ratio

The component (A), i.e., the acrylate-based oligomer, is used as thebase material of the photocurable resin composition 7. Preferredexamples of the acrylate-based oligomer may include (meth)acrylateoligomers modified by polyisoprene, polyurethane, polybutadiene, etc.(such as polyisoprene-based (meth)acrylate oligomers, polyurethane-based(meth)acrylate oligomers, and polybutadiene-based (meth)acrylateoligomers). The term “(meth)acrylate” as used herein is intended toencompass acrylate and methacrylate.

Preferred specific examples of the polyisoprene-based (meth)acrylateoligomers may include esterified products of 2-hydroxyethyl methacrylateand a maleic anhydride adduct of polyisoprene polymer (such as UC102(polystyrene-equivalent molecular weight: 17,000), Kuraray Co., Ltd.;UC203 (polystyrene-equivalent molecular weight: 35,000), Kuraray Co.,Ltd.; and UC-1 (molecular weight: about 25,000), Kuraray Co., Ltd.).

Preferred specific examples of the polyurethane-based (meth)acrylateoligomers may include aliphatic urethane acrylate oligomers (such asEBECRYL 230 (molecular weight: 5,000), Daicel-Allnex Ltd.; and UA-1,Light Chemical Industries Co., Ltd.)).

The polybutadiene-based (meth)acrylate oligomer used may be any knownoligomer.

The component (B), i.e., the acrylate-based monomer component, is usedas a reactive diluent to impart sufficient reactivity, applicationproperties, etc. to the photocurable resin composition in the process ofproducing the image display device. Examples of such an acrylate-basedmonomer may include 2-hydroxypropyl methacrylate, benzyl acrylate, anddicyclopentenyloxyethyl methacrylate.

Any known photo-radical polymerization initiator may be used as thecomponent (C), i.e., the photopolymerization initiator. Examples of thephotopolymerization initiator may include 1-hydroxy-cyclohexyl phenylketone (IRGACURE 184, BASF Japan Ltd.),2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)benzyl]phenyl}]-2-methyl-1-propan-1-one(IRGACURE 127, BASF Japan Ltd.)), benzophenone, and acetophenone.

If the amount of the photopolymerization initiator with respect to 100parts by mass of the total of the component (A), i.e., theacrylate-based oligomer, and the component (B), i.e., the acrylate-basedmonomer, is too small, the degree of curing after irradiation withultraviolet rays is insufficient. If the amount is too large, the amountof outgassing due to cleavage tends to become large, and this causes afoaming problem. Therefore, the amount of the photopolymerizationinitiator is preferably 0.1 to 5 parts by mass and more preferably 0.2to 3 parts by mass.

The photocurable resin composition may further contain component (D), aplasticizer component. The component (D), i.e., the plasticizercomponent, is used to impart cushioning properties to the cured resinlayer and to reduce the curing shrinkage ratio of the photocurable resincomposition. Under irradiation with ultraviolet rays, the plasticizercomponent does not react with the component (A), i.e., theacrylate-based oligomer component, and the component (B), i.e., theacrylate-based monomer component. The above plasticizer componentcontains a solid tackifier (1) and a liquid oil component (2).

Examples of the solid tackifier (1) may include: terpene-based resinssuch as terpene resins, terpene phenol resins, and hydrogenated terpeneresins; rosin resins such as natural rosin, polymerized rosin, rosinesters, and hydrogenated rosin; and terpene-based hydrogenated resins.In addition, non-reactive oligomers prepared by polymerizing theabove-described acrylate-based monomers to have a low molecular weightcan be used. Specific examples of such oligomers may include copolymersof butyl acrylate, 2-hexyl acrylate, and acrylic acid and copolymers ofcyclohexyl acrylate and methacrylic acid.

The liquid oil component (2) contained may be polybutadiene-based oil orpolyisoprene-based oil.

The photocurable resin composition 7 may further contain a chaintransfer agent to adjust its molecular weight. Examples of the chaintransfer agent may include 2-mercaptoethanol, lauryl mercaptan, glycidylmercaptan, mercaptoacetic acid, thioglycolic acid 2-ethylhexyl ester,2,3-dimethylmercapto-1-propanol, and an α-methylstyrene dimer.

If necessary, the photocurable resin composition 7 may further containgeneral additives such as an antioxidant and a bonding improver, forexample, a silane coupling agent.

In the photocurable resin composition 7, its curing shrinkage ratio in apost-curing step after a pre-curing step described later is suppressedto less than 3%. Basically, it is not necessary to contain theplasticizer component, but the photocurable resin composition 7 maycontain the plasticizer component (component (D)) within the range inwhich the effects of the present invention are not impaired. The totalamount of the component (A), i.e., the acrylate-based oligomercomponent, and the component (B), i.e., the acrylate-based monomercomponent, contained in the photocurable resin composition is preferably25 to 85% by mass. However, the content of the component (D), i.e., theplasticizer component, is within the range of 0 to 65% by mass.

First Embodiment

Next, a method of producing the image display device 1 described abovewill be described. As shown in FIG. 2, in the image display deviceproduction method according to a first embodiment, a resin dispenser 10is moved from one lengthwise end of the surface 6 a, which is thelight-shielding layer-formed surface of the light-transmitting covermember 6, toward the other end to apply the liquid photocurable resincomposition 7 to the surface 6 a of the light-transmitting cover member6. In this case, moving speeds are changed on the light-shielding layer3 and on the principal surface portion 4 of the surface 6 a of thelight-transmitting cover member 6.

[Application Step]

As shown in FIG. 3, the resin dispenser 10 for applying the photocurableresin composition 7 to the surface 6 a of the light-transmitting covermember 6 includes a storage portion 11 for storing the photocurableresin composition 7 and a discharge port 12 for discharging thephotocurable resin composition 7 in the storage portion 11 onto thesurface 6 a of the light-transmitting cover member 6.

In the resin dispenser 10, the discharge port 12 has a width larger thanthe width of the principal surface portion 4 of the light-transmittingcover member 6, and the width of the discharge port 12 extends acrossboth the principal surface portion 4 and each of the light-shieldinglayers 3, 3 formed on opposite sides in the direction of the width.Therefore, as shown in FIG. 4, the resin dispenser 10 applies thephotocurable resin composition 7 to the light-transmitting cover member6 such that the applied photocurable resin composition 7 extends acrossboth the principal surface portion 4 and each of the light-shieldinglayers 3, 3 formed on the opposite sides in the width direction of thelight-transmitting cover member 6.

In the resin dispenser 10, the discharge port 12 is formed so as to havethe same width in a discharge direction X of the photocurable resincomposition 7. This allows the resin dispenser 10 to discharge thephotocurable resin composition 7 uniformly over the entire width of thedischarge port 12.

As shown in FIG. 2, while the resin dispenser 10 is moved from onelengthwise end of the surface 6 a of the light-transmitting cover member6 toward the other lengthwise end with the width direction of thedischarge port 12 being parallel to the width direction of thelight-transmitting cover member 6, the liquid photocurable resincomposition 7 is extruded using an unillustrated pump and applied to theprincipal surface portion 4 and each of the light-shielding layers 3, 3so as to extend across both of them.

During the application, the resin dispenser 10 is moved at differentmoving speeds on the principal surface portion 4 formed in a centralregion in the moving direction and on the light-shielding layer 3 thatare formed at its opposite ends in the moving direction. In this manner,the resin dispenser 10 can apply the photocurable resin composition 7 inthe lengthwise direction of the light-transmitting cover member 6 suchthe height of the applied resin composition is the same on thelight-shielding layer 3 and on the principal surface portion 4, and theformed coating surface can be flat over each of the light-shieldinglayers 3, 3 and the principal surface portion 4.

As described above, the resin dispenser 10 has the discharge port 12formed to have the same width in the discharge direction X of thephotocurable resin composition 7 and discharges the photocurable resincomposition 7 uniformly over the entire width of the discharge port 12.Therefore, when the resin dispenser 10 is moved at a constant speed fromone lengthwise end of the light-transmitting cover member 6 toward theother lengthwise end, protrusions are formed on the one lengthwise endand the other lengthwise end of the light-transmitting cover member 6and near the boundaries between the light-shielding layer 3 and theprincipal surface portion 4 (see FIG. 15).

Therefore, in this embodiment, the moving speed of the resin dispenser10 is set to be high on the light-shielding layer 3 formed on the oneend and the other end of the light-transmitting cover member 6 and setto be low on the principal surface portion 4, as shown in FIG. 5.

In this manner, the resin dispenser 10 can apply the photocurable resincomposition 7 such that the height of the applied resin composition isthe same on the light-shielding layer 3 and on the principal surfaceportion 4, so that a flat coating surface can be formed in thelengthwise direction of the light-transmitting cover member 6.

The moving speed can be set to an optimal speed according to theviscosity of the photocurable resin composition 7, the height of thestep portion 5, etc. such that the photocurable resin composition 7 canbe applied evenly over the light-shielding layer 3, 3 and the principalsurface portion 4. If high protrusions are formed, the moving speed onthe light-shielding layer 3 is set to be still higher than that on theprincipal surface portion 4. In this manner, the amount of thephotocurable resin composition 7 applied to the light-shielding layer 3becomes still smaller than that to the principal surface portion 4, sothat the photocurable resin composition 7 can be applied evenly.

FIG. 6 is a graph showing the results of measurement on the surfacecoated with the photocurable resin composition 7 using a displacementsensor in each of a Conventional Example and an Example. In theConventional Example, the resin dispenser 10 was moved at a constantspeed. In the Example, the resin dispenser 10 was moved at a high speedon the light-shielding layer 3 and at a low speed on the principalsurface portion 4. The vertical axis represents height, and thehorizontal axis represents the distance from one lengthwise end of thelight-transmitting cover member 6. The moving speed of the resindispenser 10 was 16 mm/sec on the principal surface portion 4 of thelight-transmitting cover member 6 and was 24 mm/sec on thelight-shielding layer 3, i.e., 1.5 times the moving speed on theprincipal surface portion 4. The thickness of the surface coated withthe photocurable resin composition 7 was about 150 μm on the principalsurface portion 4 of the light-transmitting cover member 6 and about 40μm on the light-shielding layer 3.

As shown in FIG. 6, in the Example, since the application amount of thephotocurable resin composition 7 on the light-shielding layer 3 wasreduced, protrusions 27 on the ends of the light-transmitting covermember 6 and on the circumference of the step portion 5 became low, andthe surface was found to be flatter.

The flatness of the photocurable resin composition 7 can be measured byscanning the applied photocurable resin composition 7 with a knowndisplacement sensor that irradiates the resin composition with laserlight, LED light, ultrasonic waves, etc. to measure the height.

As described above, by adjusting the difference between the speed on thelight-shielding layer 3 and the speed on the principal surface portion 4with reference to the state of protrusions formed in the applicationstep previously performed, the application amounts can be controlled,and the speed can be set such that the photocurable resin composition 7can be applied evenly over the light-shielding layer 3 and the principalsurface portion 4. If the moving speed on the light-shielding layer 3 istoo high, recesses 28 are formed near the boundaries between thelight-shielding layer 3 and the principal surface portion 4. In thiscase, the moving speed on the light-shielding layer 3 is reduced foradjustment.

The photocurable resin composition 7 need only be applied across boththe principal surface portion 4 and the light-shielding layer 3 and isnot necessarily applied to the entire light-shielding layer 3. In orderto apply the photocurable resin composition 7 to the entirelight-shielding layer 3, the resin dispenser 10 must discharge thephotocurable resin composition 7 before it reaches the light-shieldinglayer 3. This is uneconomical, and also the application step becomescomplicated due to the occurrence of sagging of the resin etc. So longas the photocurable resin composition 7 applied is present on thelight-shielding layer 3 as shown in FIG. 4, the photocurable resincomposition 7 spreads over the entire light-shielding layer 3 in thestep of laminating the image display member 2, and therefore thelight-transmitting cover member 6 and the image display member 2 can beconnected to each other without any problem.

Therefore, it is preferable that an idling region in which the resindispenser 10 does not discharge the photocurable resin composition 7onto preferably the light-shielding layer be provided at the beginningand end of the movement of the resin dispenser 10 from one lengthwiseend of the light-transmitting cover member 6 to the other lengthwiseend.

In the step of applying the photocurable resin composition 7 describedabove, planarization is achieved by controlling the moving speed of theresin dispenser 10. However, planarization may be achieved by adjustingthe pump such that the discharged amount on the light-shielding layer 3is smaller than the discharged amount on the principal surface portion 4while the resin dispenser 10 is moved at a constant speed. However,controlling the discharge amount by adjusting the pump is morecomplicated than controlling the moving speed. Therefore, the method inwhich the moving speed of the resin dispenser 10 is controlled is betterin terms of the simplicity of the application step and yield.

In addition to moving the resin dispenser 10 relative to the fixedlight-transmitting cover member 6 as described above, the resindispenser 10 may be fixed, and the light-transmitting cover member 6 maybe moved while its speed is controlled in the manner described above.

[Pre-Curing Step]

After completion of the step of applying the photocurable resincomposition 7 to the light-transmitting cover member 6, the photocurableresin composition 7 is then irradiated with ultraviolet rays as shown inFIG. 7 to pre-cured the resin composition to thereby form a pre-curedresin layer 13 (see FIG. 8). The pre-curing is performed in order torender the photocurable resin composition 7 in liquid form less flowableso that the resin composition is prevented from running down when thecover member is turned upside down as shown in FIG. 8 to thereby improvehandleability. By pre-curing the resin composition as described above,the light-transmitting cured resin layer between the light-shieldinglayer 3 and the image display member can be sufficiently photo-curedwithout being excluded from the space between the light-shielding layer3 and the image display member, and curing shrinkage can also bereduced. The degree of pre-curing is such that the curing rate (gelfraction) of the pre-cured resin layer 13 is preferably 10 to 80% andmore preferably 30 to 60%. The curing rate (gel fraction) is a valuedefined as the ratio of the amount of (meth)acryloyl groups present inthe photocurable resin composition 7 after irradiation with ultravioletrays to the amount of (meth)acryloyl groups present before irradiationwith ultraviolet rays (the ratio of the amount consumed). This showsthat the larger the value of the curing rate is, the higher the degreeof progress of curing is.

The curing rate (gel fraction) can be computed by substituting, into thefollowing formula (1), the height (X) of an absorption peak at 1640 to1620 cm⁻¹ from the base line in an FT-IR measurement chart of the resincomposition layer before irradiation with ultraviolet rays and theheight (Y) of the absorption peak at 1640 to 1620 cm⁻¹ from the baseline in an FT-IR measurement chart of the resin composition layer afterirradiation with ultraviolet rays.

Curing Rate (%)={(X−Y)/X}×100  (1)

No particular limitation is imposed on the type and power of the lightsource, the cumulative light amount, etc. when the irradiation withultraviolet rays is performed, so long as the resin composition can bepre-cured such that the curing rate (gel fraction) is preferably 10 to80%. Any known conditions for a photo-radical polymerization process for(meth)acrylate by irradiation with ultraviolet rays can be used.

Preferably, the conditions for irradiation with ultraviolet rays areselected such that the curing rate is within the range described aboveand no sagging and deformation of the pre-cured resin layer 13 occurduring a lamination operation described later. The conditions underwhich the sagging and deformation do not occur may be expressed in termsof viscosity, and the viscosity is 20 Pa·S or more (cone-platerheometer, 25° C., cone/plate C35/2, number of revolutions: 10 rpm).

Preferably, the conditions for irradiation with ultraviolet rays areselected such that the curing rate is within the range described aboveand the pre-cured resin layer 13 can maintain its surface stickiness(tackiness) during the lamination operation described later. Theconditions under which the stickiness can be maintained may be expressedin terms of a measurement value obtained by a probe tack method (RHESCAmethod: a method including placing a sample with its adhesive surfacefacing up, pressing the probe against the adhesive surface from above,and then peeling the probe) using a tacking tester (TAC-1000, RHESCACo., Ltd.), and the measurement value is 30 N/mm² or more (see “Methodof measuring physical properties of adhesive material” inhttp://www.rhesca.co.jp/main/technical/technical.html).

[Laminating Step]

Next, as shown in FIG. 9, the light-transmitting cover member 6 islaminated to the image display member 2 with the pre-cured resin layer13 facing thereto. The lamination can be performed by applying pressureat 10° C. to 80° C. using a known compression bonding device.

[Post-Curing Step]

Next, as shown in FIG. 10, the pre-cured resin layer 13 held between theimage display member 2 and the light-transmitting cover member 6 isirradiated with ultraviolet rays to post-cure the pre-cured resin layer13. If necessary, the resin layer between the light-shielding layer ofthe light-transmitting cover member 6 and the image display member 2 isirradiated with ultraviolet rays to post-cure the resin layer. In thismanner, the image display member 2 and the light-transmitting covermember 6 are laminated through a light-transmitting cured resin layer 8to thereby obtain an image display device 1.

The post-curing in this step is performed in order to sufficiently curethe pre-cured resin layer 13 to thereby bond and laminate the imagedisplay member 2 to the light-transmitting cover member 6. The degree ofpost-curing is such that the curing rate (gel fraction) of thelight-transmitting cured resin layer 8 is preferably 90% or higher andmore preferably 95% or higher.

The degree of light transmitting properties of the light-transmittingcured resin layer 8 need only be such that an image formed on the imagedisplay member 2 is visible.

Second Embodiment

Next, another method of producing the above-described image displaydevice 1 will be described. The image display device production methodaccording to a second embodiment includes applying the liquidphotocurable resin composition 7 to the surface 6 a of thelight-transmitting cover member 6 using a resin dispenser 15. In theresin dispenser 15, the width between opposite end portions 14 a of adischarge port 14 that face the light-shielding layer 3 of thelight-transmitting cover member 6 is made larger than the width of acentral portion 14 b of the discharge port 14 that faces the principalsurface portion 4.

As shown in FIG. 11, the resin dispenser 15 includes a storage portion16 for storing the photocurable resin composition 7 and the dischargeport 14 for discharging the photocurable resin composition 7 in thestorage portion 16 toward the surface 6 a of the light-transmittingcover member 6.

In the resin dispenser 15, as in the above-described resin dispenser 10,the discharge port 14 has a width larger than the width of the principalsurface portion 4 of the light-transmitting cover member 6, and thewidth of the discharge port 14 extends across both the principal surfaceportion 4 and each of the light-shielding layers 3, 3 formed on oppositesides in the direction of the width. Therefore, the resin dispenser 15applies the photocurable resin composition 7 to the light-transmittingcover member 6 such that the applied photocurable resin composition 7extends across both the principal surface portion 4 and each of thelight-shielding layers 3, 3 formed on opposite sides in the widthdirection (see FIG. 4).

In the resin dispenser 15, the width between the opposite end portions14 a of the discharge port 14 that face the light-shielding layer 3 ofthe light-transmitting cover member 6 is larger than the width of thecentral portion 14 b that faces the principal surface portion 4.Specifically, a tapered surface is formed in each of the opposite endportions 14 a, so that the width between the tapered surfaces graduallyincreases from the central portion 14 b. Accordingly, in the resindispenser 15, the width between the opposite end portions 14 a of thedischarge port 14 increases in the discharge direction X of thephotocurable resin composition 7, and the photocurable resin composition7 supplied from the central portion 14 b is distributed toward theopposite end portions 14 a and then discharged. Therefore, with theresin dispenser 15, the discharge amount on the light-shielding layer 3can be made smaller than the discharge amount on the principal surfaceportion 4.

While the resin dispenser 15 is moved from one lengthwise end of thesurface 6 a of the light-transmitting cover member 6 toward the otherlengthwise end with the discharge port 14 being parallel to the widthdirection of the light-transmitting cover member 6, the liquidphotocurable resin composition 7 is extruded using an unillustrated pumpand applied to the principal surface portion 4 and each of thelight-shielding layers 3, 3 so as to extend across both of them.

In this case, since the width between the opposite end portions 14 a ofthe discharge port 14 of the resin dispenser 15 that face thelight-shielding layer 3 of the light-transmitting cover member 6 islarger than the width of the central portion 14 b facing the principalsurface portion 4, the photocurable resin composition 7 can be appliedsuch that the height of the applied resin composition is the same on thelight-shielding layer 3 and on the principal surface portion 4 over theentire width of the light-transmitting cover member 6, so that a flatcoating surface can be formed.

The opposite end portions 14 a of the discharge port 14 of the resindispenser 15 are formed to have an optimal angle and an optimal heightaccording to the viscosity of the photocurable resin composition 7, theheight of the step portion 5, etc. such that the photocurable resincomposition 7 can be applied evenly over each of the light-shieldinglayers 3, 3 and the principal surface portion 4.

[Height of Resin Dispenser 15]

Preferably, in the resin dispenser 15, the height H of the front end ofthe discharge port 14 from the surface 6 a of the light-transmittingcover member 6 is adjusted when the photocurable resin composition 7 isdischarged. As shown in FIG. 12, if the height H of the front end of thedischarge port 14 from the surface 6 a of the light-transmitting covermember 6 is too large, the photocurable resin composition 7 dispersedtoward each of the opposite end portions 14 a is concentrated in oneplace by tension before applied to the light-shielding layer 3 andaccumulated near a widthwise end portion of the light-transmitting covermember 6. Therefore, a protrusion of the photocurable resin composition7 is formed near the end portion of the light-transmitting cover member6 (see FIG. 13).

In contrast, if the height H of the front end of the discharge port 14from the surface 6 a of the light-transmitting cover member 6 is toolow, the photocurable resin composition 7 does not sufficiently spreadfrom the opposite end portions 14 a toward the light-shielding layer 3,and a recess extending from the light-shielding layer 3 to the principalsurface portion 4 is formed (see FIG. 13).

Therefore, in the resin dispenser 15, if a high protrusion is formed,the front end of the discharge port 14 is brought closer to the surface6 a of the light-transmitting cover member 6. If a recess 28 is formed,the front end of the discharge port 14 is moved away from the surface 6a of the light-transmitting cover member 6.

As described above, the resin dispenser 15 adjusts the height H of thefront end of the discharge port 14 from the principal surface 6 a of thelight-transmitting cover member 6 with reference to the state ofirregularities generated near the boundaries between the principalsurface portion 4 and the light-shielding layer 3 in the applicationstep previously performed. In this manner, the resin dispenser 15 cancontrol the amount of the photocurable resin composition 7 applied andcan thereby set the height H such that the photocurable resincomposition 7 can be applied evenly over the light-shielding layer 3 andthe principal surface portion 4.

FIG. 13 is a graph showing the results of measurement, using adisplacement sensor, on surfaces coated with the photocurable resincomposition 7 using the resin dispenser 15. The measurement wasperformed with the front end of the discharge port 14 placed atdifferent heights H from the surface 6 a of the light-transmitting covermember 6, and each coated surface was measured with the displacementsensor. The vertical axis represents height, and the horizontal axisrepresents the distance from one widthwise end of the light-transmittingcover member 6. As can be seen from FIG. 13, when the height H of thefront end of the discharge port 14 from the principal surface 6 a of thelight-transmitting cover member 6 is too high, i.e., 190 μm or 200 μm, aprotrusion is formed near a widthwise end of the light-transmittingcover member 6. When the height is too low, i.e., 160 μm or 170 μm, arecess is formed. When the height H is 180 μm, the photocurable resincomposition 7 can be applied substantially evenly.

The resin dispenser 15 can apply the photocurable resin composition 7evenly near the opposite widthwise end portions of thelight-transmitting cover member 6 and the boundaries between thelight-shielding layer 3 and the principal surface portion 4 irrespectiveof the moving speed. Therefore, as in the above-described applicationstep using the resin dispenser 10, when the resin dispenser 15 is movedfrom one lengthwise end of the light-transmitting cover member 6 towardthe other lengthwise end to apply the liquid photocurable resincomposition 7 to the surface 6 a of the light-transmitting cover member6, moving speeds are changed on the light-shielding layer 3 and on theprincipal surface portion 4 of the surface 6 a the light-transmittingcover member 6. In this manner, the photocurable resin composition 7 canbe applied evenly in the lengthwise and widthwise directions of thelight-transmitting cover member 6.

Third Embodiment

Next, another method of producing the image display device 1 describedabove will be described. In the image display device production methodaccording to a third embodiment, the surface tension of the photocurableresin composition 7 is adjusted to apply the resin composition evenly.The photocurable resin composition 7 in the third embodiment contains anacrylate-based oligomer component (component (A)), an acrylate-basedmonomer component (component (B)), a photopolymerization initiator(component (C)), and a plasticizer component (component (D)), and aleveling agent may be added. In this manner, the surface can be adjusted(reduced), and the occurrence of protrusions near the boundaries betweenthe light-shielding layer 3 and the principal surface portion 4 can bereduced.

No particular limitation is imposed on the leveling agent, andsiloxane-based leveling agents such as product name BYK378 (manufacturedby BYK Japan KK) and product name LH-90 (Kusumoto Chemicals, Ltd.) canbe used for the composition formed from (A) to (D) above. The amount ofthe leveling agent added to the photocurable resin composition 7 ispreferably 0.1 to 1.0 wt % and particularly preferably 0.2 to 0.6 wt %.

The photocurable resin composition 7 has a surface tension of 30 to 35mN/m or higher when no leveling agent is added, and the addition of theleveling agent allows the surface tension to be 30 mN/m or less,particularly within the range of 28 to 24 mN/m.

EXAMPLES

Examples of the third embodiment will next be described.

First, a glass plate with a size of 45 (w)×80 (1)×0.4 (t) mm wasprepared. A 4 mm-wide light-shielding layer was applied to the entirecircumferential edge portion of the glass plate to a dry thickness of 40μm using a thermosetting black ink (MRX ink, Teikoku Printing Inks Mfg.Co., Ltd.) by a screen printing method and then dried to prepare alight-shielding layer-attached glass plate.

The photocurable resin composition in Example 1 was prepared byuniformly mixing 40 parts by mass of an acrylic-based oligomer having apolyisoprene skeleton (UC203, Kuraray Co., Ltd.), 20 parts by mass ofdicyclopentenyloxyethyl methacrylate (FA512M, Hitachi Chemical Co.,Ltd.), 3 parts by mass of hydroxypropyl methacrylate (HPMA, Nippon KaseiChemical Co., Ltd.), 15 parts by mass of tetrahydrofurfuryl acrylate(Light Ester THF, Kyoeisha Chemical Co., Ltd.), lauryl acrylate (LightEster L, Kyoeisha Chemical Co., Ltd.), 20 parts by mass of apolybutadiene polymer (Polyoil 110, Degussa), 45 parts by mass of ahydrogenated terpene resin (P85, Yasuhara Chemical Co., Ltd.), and 4parts by mass of a photopolymerization initiator (Irg184D, BASF JapanLtd.). The surface tension of the photocurable resin compositionaccording to Example 1 was 35 mN/m.

A photocurable resin composition according to Example 2 was prepared byadding 1 part by mass of a siloxane-based leveling agent BYK378(manufactured by BYK Japan KK) to the composition in Example 1. Thesurface tension of the photocurable resin composition according toExample 2 was 25 mN/m.

Next the photocurable resin compositions according to Examples 1 and 2were discharged using the above-described resin dispenser 15 onto theentire light-shielding layer-formed surfaces of differentlight-shielding layer-attached glass plates to form photocurable resincomposition films each having an average thickness of 150 μm. Theapplication conditions of the resin dispenser 15 are as follows. Theapplication was performed at 16 mm/sec on the principal surface portionof the light-shielding layer-attached glass plate and at a speed higherby 1.5 times the above speed, i.e., 24 mm/sec, on the light-shieldinglayer.

The application was performed at 16 mm/sec on both the principal surfaceportion of the glass plate and the light-shielding layer, and this wasused as Example 3.

This photocurable resin composition film was formed over substantiallythe entire light-shielding layer as shown in FIG. 1, and the surfacecoated with the photocurable resin composition 7 had a thickness ofabout 150 μm on the principal surface portion 4 of thelight-transmitting cover member 6 and about 40 μm on the light-shieldinglayer 3.

The flatness of each of the photocurable resin composition films usingthe photocurable resin compositions 7 according to Examples 1 and 2 wasmeasured using a displacement sensor. The heights of protrusions on theprincipal surface portion 4 from the coated surface were 0.02 mm or lessin each of Examples 1 and 2, and a reduction in height of theprotrusions was achieved.

The protrusions formed on the photocurable resin composition filmaccording to Example 2 were lower by about 0.01 mm than the protrusionsformed on the photocurable resin composition film according toExample 1. This is because since the leveling agent was added to thephotocurable resin composition 7 according to Example 2 and thereforeits surface tension was 25 mN/m, which was lower than that of thephotocurable resin composition 7 in Example 1, the protrusions werespontaneously flattened. Specifically, it was found that it is effectiveto add a leveling agent to the photocurable resin composition 7 to lowerthe surface tension thereof.

Also in Example 3, protrusions lower by 0.003 to 0.007 mm than those ofthe protrusions formed on the photocurable resin composition filmaccording to Example 1 were formed. As described above, even when thespeed of the resin dispenser is unchanged, protrusions can be lowered byadding a leveling agent.

REFERENCE SIGNS LIST

-   1 image display device-   2 image display member-   3 light-shielding layer-   4 principal surface portion-   5 step portion-   6 light-transmitting cover member-   7 photocurable resin composition-   8 light-transmitting cured resin layer-   10, 15 resin dispenser-   11, 16 storage portion-   12, 14 discharge port-   13 pre-cured resin layer-   14 a opposite end portions-   14 b central portion-   27, 27 a, 27 b protrusion-   28 recess

1. A method of producing an image display device in which an imagedisplay member and a light-transmitting cover member having a principalsurface portion and a circumferential edge portion on which alight-shielding layer is formed with a step portion formed between theprincipal surface portion and the circumferential edge portion arelaminated through a light-transmitting resin layer formed from a liquidoptical resin composition so that a light-shielding layer-formed surfaceof the light-transmitting cover member is arranged to face the imagedisplay member, the method comprising: moving a resin dispenser from oneend of the light-shielding layer-formed surface of thelight-transmitting cover member toward the other end thereof to applythe liquid optical resin composition to the principal surface portionand a part of the light-shielding layer of the light-transmitting covermember so as to extend across both of them, and upon the moving,providing an idling region in which the resin dispenser does notdischarge the optical resin composition on a part of the light-spielinglayer; laminating the light-shielding layer-formed surface of thelight-transmitting cover member to the image display member through theapplied optical resin composition; and curing the applied optical resincomposition held between the image display member and thelight-transmitting cover member, wherein the optical resin compositioncomprises an acrylate-based oligomer component, an acrylate-basedmonomer component, a photopolymerization initiator, a plasticizercomponent and a leveling agent, and a surface tension of the opticalresin composition is adjusted within the range of 24 to 28 mN/m.
 2. Themethod according to claim 1, wherein the leveling agent contains asiloxane component, and an amount of the siloxane component added to theoptical resin composition is within 0.1 to 1.0 wt %.